As techniques for generating desired gaits of a mobile robot, such as a bipedal mobile robot, one disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-326173 (patent document 1) and one disclosed in PCT international publication WO/03/057427/A1 (patent document 2) have been proposed by the present applicant. According to the techniques disclosed in these documents, an instantaneous desired gait composed of an instantaneous value of a desired motion (instantaneous desired motion) of a robot and an instantaneous value of a desired floor reaction force (instantaneous desired floor reaction force) is sequentially created using a first dynamic model representing a relationship between a motion of the robot (position and posture of each part) and a floor reaction force such that a required dynamic balance condition (a condition, such as the one in which a translational force component of a floor reaction force reaches a desired value or a floor reaction force moment about a certain point reaches a desired value) on the first dynamic model is satisfied. Then, the instantaneous desired gait is input to a second dynamic model wherein a part of the instantaneous desired motion (desired body position/posture, a desired moment about a desired ZMP, or the like) is corrected so as to generate a final instantaneous desired gait in a time series manner.
In this case, a model having high linearity is generally used as the first dynamic model. Creating instantaneous desired gaits by using a dynamic model with high linearity makes it possible to efficiently and promptly create gaits (gaits that allow stable motions of the robot to continue) that connect to or gradually approximate normal gaits, which are virtual cyclic gaits. As a result, instantaneous desired gaits of the robot can be sequentially generated in real time while performing actual motions of the actual robot.
However, a dynamic model with high linearity generally tends to exhibit relatively low dynamic accuracy in a variety of operations of a robot. In other words, the dynamics of the robot on the dynamic model is apt to produce errors with respect to the actual dynamics of the actual robot. For this reason, if the instantaneous desired gaits created using the first dynamic model are directly applied to the actual robot to operate the actual robot, then the dynamic balance condition guaranteed on the first dynamic model fails to be satisfied on the actual robot, frequently leading to unstable motions of the actual robot.
Hence, according to the techniques disclosed in the aforesaid patent documents 1 and 2, a part of an instantaneous desired gait created using the first dynamic model is further corrected using the second dynamic model. In this case, a model having higher dynamic accuracy than the first dynamic model is used as the second dynamic model. This makes it possible to generate gaits having higher dynamic accuracy (closer to the dynamics of the actual robot) than the gaits created using the first dynamic model.
Meanwhile, since the first dynamic model tends to exhibit low dynamic accuracy, as mentioned above, dynamic errors may be relatively large, depending on the type of gaits to be generated. More specifically, in a case where a gait is generated to make a robot perform a motion in which an inertial force not assumed (considered) in the first dynamic model is produced, the error frequently increases. For example, in a case where a 3-mass-point dynamic model having mass points, one each corresponding to the body and a portion near the distal portion of each leg of a bipedal mobile robot, respectively, or a 1-mass-point dynamic model having the mass point only in the body of a robot is used as the first dynamic model, if a motion in which especially the knee joint of each leg is bent is carried out relatively quickly, then the dynamic error will be relatively large because of an influence of a change in an inertial force involved in the motion. As a result, an instantaneous desired gait created using the first dynamic model sometimes becomes unduly inappropriate in securing continuous stability of the robot. In such a case, there has been a danger in that even if the instantaneous desired gait is corrected using the second dynamic model, the correction cannot be properly made, and the corrected instantaneous desired gait exhibits low stability allowance or diverges, failing to secure continuous stability of the robot.
The present invention has been made in view of the background described above, and it is an object thereof to provide a gait generating device of a mobile robot that is capable of properly correcting, without using a dynamic model (without using a differential equation or an integral equation that represents a relationship between motion and force), the motion of an instantaneous desired gait created using a dynamic model, thereby improving the dynamic accuracy of an instantaneous desired gait including the corrected motion.